The present invention relates generally to a system and method for placing one or more implantable cardiac leads within a coronary artery or cardiac vein; and more particularly, relates to a system and method that may be used to implant an electrode array within one or more vessels of a body using a single-pass procedure.
Implantable medical electrical stimulation and/or sensing leads are well known in the fields of cardiac stimulation and monitoring, including cardiac pacing and cardioversion/defibrillation. In the field of cardiac stimulation and monitoring, endocardial leads are placed through a transvenous route to locate one or more sensing and/or stimulation electrodes along, or at the distal end of, the lead in a desired location within a heart chamber or interconnecting vasculature. In order to achieve reliable sensing of the cardiac electrogram and/or to apply stimulation that effectively paces or cardioverts the heart chamber, it is necessary to accurately position the electrode surface against the endocardium or within the myocardium at the desired site and fix it during an acute post-operative phase until fibrous tissue growth occurs.
The pacemaker or defibrillator implantable pulse generator (IPG) or the monitor is typically coupled to the heart through one or more of such endocardial leads. The proximal end of such a lead is typically formed with a connector that connects to a terminal of the IPG or monitor. The lead body typically comprises one or more insulated conductive wires surrounded by an insulating outer sleeve. Each conductive wire couples a proximal lead connector element with a distal stimulation and/or sensing electrode.
In order to implant an endocardial lead within a heart chamber, a transvenous approach is utilized wherein the lead is inserted into and passed through the subclavian, jugular, or cephalic vein and through the superior vena cava into the right atrium or ventricle. An active or passive fixation mechanism is incorporated into the distal end of the endocardial lead and deployed to maintain the distal end electrode in contact with the endocardium position.
More recently, endocardial pacing and cardioversion/defibrillation leads have been developed that are adapted to be advanced into the coronary sinus and coronary veins branching therefrom in order to locate the distal electrode(s) adjacent to the left ventricle or the left atrium. The distal end of such coronary sinus leads is advanced through the superior vena cava, the right atrium, the valve of the coronary sinus, the coronary sinus, and may further be advanced into a coronary vein communicating with the coronary sinus, such as the great vein. Typically, coronary sinus leads do not employ any fixation mechanism and instead rely on the close confinement within these vessels to maintain each electrode at a desired site.
Routing an endocardial lead along a desired path to implant the electrode or electrodes in a desired implantation site, either in a chamber of the heart or in the selected cardiac vein or coronary artery, can be difficult. This is particularly true for steering leads through the coronary sinus and into a branching vein on the left myocardium. Anomalies in the vascular anatomy and the number of branch veins associated with the anatomy make locating the desired path challenging.
Several common approaches have been developed to place electrodes within the vascular system of the heart. According to one approach, a guide catheter is steered into the desired location in the vasculature. A lead is then fed through the inner lumen of the catheter such that the lead electrode(s) are positioned at predetermined locations. The guide catheter may then be withdrawn. This type of approach is described in commonly assigned U.S. Pat. Nos. 6,006,137, 5,246,014, and 5,851,226 incorporated herein by reference. The described systems employ highly flexible, catheters surrounding the lead body. One difficulty with systems of this nature is that the lead body may not be pushable and trackable enough to be advanced through the catheter lumen. This is particularly true when the catheter is positioned within the torturous curves of a patient""s vasculature system. The problem is exaggerated when very small leads having a diameter of 4 French or less are employed for use in the coronary sinus or associated vasculature.
Another approach to lead placement involves the use of a guide wire that is steered into a desired location within the vasculature. The lead body is then tracked over the wire and the wire is withdrawn. According to this design, the guide wire passes through an inner lumen of the lead for an entire length of the lead. This results in a significant amount of friction that can make lead placement difficult. Additionally, since the lead must include an inner lumen for the guide wire, the size of the lead is at least somewhat dictated by the size of the guide wire. Moreover, to accomplish lead placement in this manner, the lead must again be both pushable and trackable enough to allow it to be advanced over the guide wire through the tortuous curves of the vasculature.
Yet another approach is described in commonly-assigned U.S. Pat. No. 5,902,331 to Bonner et al. The disclosed system includes a pusher mechanism that is adapted to slidably engage a guidewire that has previously been placed at a desired implant site. The pusher mechanism couples to a lead body to allow the pusher to guide the lead over the guidewire to the desired implant site. The lead body may then be released from the pusher, and the pusher and guidewire are withdrawn from the body.
One problem with the system and method disclosed in the ""331 patent discussed above is that the system is not adapted to efficiently delivery multiple leads. To deliver more than a single lead using a system with a pusher mechanism involves withdrawing the pusher from the body, loading an additional lead on the guidewire, and deploying the lead from the guidewire in the manner discussed above. Because the pusher must be withdrawn from the body each time an additional lead is loaded onto the guidewire, the time of implant is significantly increased. Additional handling of the guidewire outside the body also increases the risk of infection. Moreover, the position of the distal tip of the guidewire must be moved to a new implant site before any additional lead is delivered, increasing the variability associated with the selected site of implant.
The use of multiple-lead electrode arrays is particularly desirable in the delivery defibrillation and cardioversion therapies. For example, by placing multiple, spaced apart defibrillation electrodes within the coronary sinus or a branch vein such as the Middle Cardiac Vein (MCV), the defibrillation threshold can be reduced as compared to a system using a single electrode for the delivery of electrical stimulation.
What is needed, therefore, is an improved system and method for placing leads within coronary arteries and cardiac veins such as the Middle Cardiac Vein (MCV) that is readily adapted for placing multiple leads at respective predetermined implant sites.
An improved system and method that is capable of delivering multiple electrode assemblies to predetermined implant sites within a body is disclosed. The system includes an elongated tubular member such as an introducer sheath. The introducer includes an elongated channel along at least a distal end portion of the introducer. The elongated channel opens to the exterior surface of the introducer through an elongated slot. One or more electrode assemblies may be retained within the elongated channel such that the leads coupled to the electrode assemblies exit the introducer via the elongated slot.
The elongated introducer further includes a lumen that is in fluid communication with the channel through openings, or gaps, between the lumen and the channel. The electrode assemblies are loaded within the channel at predetermined positions with respect to the openings. A distal end of a stiffening member such as a stylet may then be advanced within the lumen, inserted through a selected opening to enter the channel, and coupled to an associated electrode assembly. The stiffening member is further advanced within the channel to push the electrode assembly from the distal end of the channel at a predetermined implant site. The lead coupled to the electrode assembly is allowed to trail the electrode assembly through the slot as the electrode assembly is deployed.
To deploy any additional electrode assemblies, the stiffening member is retracted until the distal end of the stiffening member is again located within the lumen. The introducer may then be re-positioned at a second implant site, which is preferably located at a proximal position within a vessel as compared to the first implant site. The stiffening member distal end is again positioned through a different one of the openings to engage a second electrode assembly. The second electrode assembly is deployed in a manner similar to that discussed above. Additional electrode assemblies may be deployed in a similar manner. Thus the inventive system and method allows an array of electrodes to be positioned within one or more vessels within a body without having to withdraw an introducer or a stiffening member from the body during the implant procedure to re-load additional electrodes.
According to one aspect of the invention, the stiffening member may include a cant, or bend, at the distal end. This cant is adapted to readily allow the distal end of the stiffening member to extend from the lumen into the channel. The stiffening member is preferably formed of a material such as a superelastic alloy that may be deformed without losing an original pre-formed shape. This allows the stiffening member to flex as the body of the stiffening member is advanced through a selected opening from the lumen to the channel as an electrode is deployed.
In one embodiment, the proximal end of stiffening member includes one or more markers to aid a user in locating the openings of the lumen prior to electrode deployment. For example, in one embodiment, the markers are visible indicators at a proximal end of a stylet that may be aligned so that distal end of the stylet is adjacent a selected opening. Alternatively, a handle coupled to introducer could include a travel limiter that engages a protrusion in the stiffening member to indicate when alignment has occurred.
Many different types of electrode assemblies may be adapted for use with the current invention. In one embodiment, the electrode assemblies are self-expanding electrodes that include fixation means that expand to contact one or more walls of a vessel. This allows the electrode assembly to be retained at a predetermined site of implant until tissue in-growth begins.
The electrode assemblies of the current invention further include a mechanism for engaging the stiffening member. For example, the electrode assembly may include an inner lumen to receive the distal end of the stiffening member. The inner lumen may include a key to engage a keyed structure of the stiffening member. According to one embodiment, the key may be adapted to receive the distal end of a bladed stylet assembly.
As described above, the stiffening member is coupled to the electrode assembly prior to deploying the electrode assembly. The stiffening member may then be advanced in a distal direction to cause the electrode assembly to exit the channel of the introducer. In an embodiment in which the electrode assembly is self-expanding, the electrode assembly expands upon exiting the channel. When a proximal force is then applied to the stiffening member, the distal end of the introducer de-couples the electrode assembly from the stiffening member.
According to another aspect of the invention, the distal end of the introducer may include an inflatable collar that is in fluid communication with an inflation lumen. Using a port at the proximal end of the introducer, the inflatable collar may be expanded to retain the introducer at a predetermined location within a vessel during electrode deployment. The introducer may further include a second port that is capable of providing fluid to the channel carrying the electrode assemblies. For example, a saline drip may be coupled to the second port so that the channel remains lubricious during the implant procedure. This further aids in minimizing thrombus formations.
The inventive system may further include a sheath for binding the leads of the electrode assemblies together to minimize wear and also reduce tissue abrasion. The sheath may be formed of loosely braided fibers. The tube may be anchored to the distal end of the introducer with a tether such as may be formed of surgical suture material. After all electrode assemblies are placed, the proximal end of the tube is tightened to hold the leads snug. A weakened spot in the tether may be provided to allow the tether to be de-coupled from the introducer upon application of adequate tension. This allows the flexible tube to remain in place around the leads after the introducer is withdrawn from the body.
Other scopes and aspects of the current invention will become apparent to those skilled in the art from the accompanying detailed description and the drawings.